The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Tetrapod Tracks on Valentia Island

These tracks in the exposed rocks at the coast on Valentia Island, County Kerry, Republic of Ireland, were created 385 million years ago by a tetrapod as it waddled across soft mud probably near a coastal river. The animal was lizard-like and is one of the earliest known vertebrates to be able live outside the ocean and walk on land. In fact, these are the oldest in situ vertebrate fossil tracks in the world. Its vertebrate ancestors were fish that had begun to live and breed in shallow waters at the edge of rivers. They developed the ability to breathe out of water and once their fins had evolved into legs they were ready to colonize the land.

Before about 500 million years ago, animal life was confined to the oceans because fatal doses of solar ultraviolet radiation (UV) were still bombarding the Earth’s surface. However, the oxygenation of the atmosphere by phytoplankton in the oceans and primitive UV-tolerant land plants led to a buildup in concentrations of ozone in the upper atmosphere, sufficient to reduce the level of incoming ultraviolet light.

Surprisingly the tracks above were discovered as recently as 1992 as the Atlantic Ocean removed overlying layers of rock. The ocean's same erosive forces will remove the tracks forever in the not too distant future. Photo taken on April 9, 2017.